Second graders learn to add and subtract 10 and 100 in their heads — by changing just one digit — a mental-math superpower built on understanding place value.
Students will be able to…
What is 234 + 100? You can answer in your head in one second — without adding it out! What is the secret?
Project this and tap each idea. Have students see how adding 10 or 100 changes just one digit — mental math made easy!
Tap any phase to open the teacher moves and student actions.
What is 234 + 100? Can you answer without adding it all out?
Teacher models.
Class uses the Mental Math Explorer.
Students do mental math.
One mental-math problem.
Aligned to the Common Core State Standards for Mathematics.
Mentally add 10 or 100 to a number, and subtract 10 or 100, within 900.
Understand three-digit place value.
Fluently add and subtract within 100.
Use place-value structure to compute mentally.
Preview the three formative checks. Tap “Sample answer” to see what mastery looks like — hide them before you print for students.
Have students do a chain in their heads — like 200, +100, +10, −10 — saying each answer aloud. A printable mental-math sheet is in the Math library.
Tap a card to flip it, then rate whether you knew it. Built from this lesson’s vocabulary.
A quick self-check with instant feedback, drawn from this lesson’s key terms.
A print-and-go review sheet with a built-in answer key. Tap “Show answer key” to reveal answers, or print the clean version for students.